Losing access to Galileo has an advantage
Don't distress too much about this. Losing access to the high accuracy signal on Galileo means that the government's plans for road pricing (AKA spying on your every car journey) will be kicked into the long grass.
As for our contributions so far, and the future budgets we have agreed, if we don't get access to Galileo we should simply deduct our contribution from any leaving settlement.
The EU. The only project you can invest billions in, then when you leave, you still owe money!